Conventionally, an image forming apparatus using electrophotography (e.g., copying machine, printer, facsimile, and multi-functional apparatus) includes a developing unit, which uses a two-component developing agent composed of toners and carriers (and additives, as required), for example.
In such image forming apparatus, fresh agent such as toner and carrier is supplied to the developing unit, as required, with a method called trickle developing method.
In general, when toners are consumed by image forming operations, fresh toners are supplied to the developing unit through a toner supply port of the developing unit, as required.
An agitation member such as transport screw agitatingly mixes such fresh toners, supplied into the developing unit, with a developing agent in the developing unit.
Then, such agitatingly mixed developing agent is supplied to a developing roller. The developing agent carried-up on the developing roller may be regulated to a given amount by a doctor blade.
Toners in such two-component developing agent adhere a latent image formed on a photoconductive drum when the developing roller comes to a developing area, at which the developing roller and photoconductive drum face each other.
In such developing process, carriers in the two-component developing agent may not be consumed during the developing process but remains in the developing unit, by which such carriers may degrade its property over the time due to several factors such as stress received by an agitation movement in the developing unit.
Specifically, a coating layer on carrier may be abraded or peeled off due to agitation and mixing of carriers in the developing unit for a longer period of time, which may lead to a degradation of charge-ability of carriers (so called “peel-off” phenomenon), or toners and additives may adhere on surface of carriers, which may lead to a degradation of charge-ability of carriers (so called “spent” phenomenon).
The above-mentioned trickle developing method may be used to prevent an image quality degradation of a printed image caused by aging (or degradation) of carriers.
Specifically, fresh carriers (or fresh two-component developing agent) are supplied into the developing unit, as required, and a part of two-component developing agent used in the developing unit is ejected to an outside of the developing unit, as required, to reduce an amount of degraded carriers in the developing unit. With such method, the amount of carriers and charge-ability of carriers in the developing unit may be maintained at a preferable level.
An image forming apparatus using such trickle developing method may stabilize an image quality of printed image over the time compared to another image forming apparatus, which requires a replacement of developing unit or carriers to a new one whenever an aging (or degradation) of carriers may occur.
One related image forming apparatus, using a trickle developing method, includes a carrier container, a developing unit, and a transport route extended from the carrier container to the developing unit. Fresh carriers in the carrier container are transported to the developing unit through the transport route, which has a coil screw (or transport screw) therein.
Specifically, such coil screw, provided inside the transport route (e.g., tube) connecting the carrier container and the developing unit, can transport carriers with mechanical (or physical) transportability of coil screw.
As for such image forming apparatus, even if the carrier container and the developing unit are distanced apart with each other, carriers may be transported with mechanical (or physical) transportability of coil screw.
However, such coil screw may not be used for a transport route having a complexed bending portion or a transport route that extends from a lower position to a higher position (e.g., vertical or inclined route) because carries have to move in a upward direction in the vertical or inclined route against gravity effect, which acts on carries toward a downward direction.
Therefore, an agent transport unit having coil screw may restrict a freedom of space layout in an image forming apparatus.
Furthermore, fresh carriers may receive mechanical (or physical) stress from the coil screw when the coil screw transports the fresh carriers, and thereby a coating layer on such fresh carriers may be abraded or peeled off, which is not a favorable phenomenon.
Another related image forming apparatus, using a trickle developing method, includes a toner transport unit, which transports toners stored in a toner container to a developing unit with a screw pump (e.g., mohno-pump).
Such toner transport unit connects the toner container and the developing unit with a transport route made of flexible tube, by which a freedom of space layout in the image forming apparatus may be improved.
A pump such as air pump and screw pump may transport carriers by supplying a gas flow (e.g., airflow) in the transport route, which connects the carrier container and the developing unit, without causing mechanical (or physical) stress to carriers.
Even in such configuration, a smooth transportation of carriers through the transport route (e.g., transport tube) may be degraded, and the carriers may clog or stagnate the transport route (e.g., transport tube).
If carriers clog or stagnate the transport route (e.g., transport tube), the transport route may be choked at such clogging or stagnating portion, by which the carriers may not be effectively supplied to the developing unit.
Similarly, such drawback may occur when transporting toner or a two-component developing agent in a transport route.